Fabricating semiconductor devices such as logic and memory devices typically includes processing a substrate such as a semiconductor wafer using a large number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. As semiconductor device size become smaller and smaller, it becomes critical to develop enhanced photomask inspection and review devices and procedures.
Actinic and non-actinic optical microscopy and standard E-beam inspection systems have been used to inspect photomasks. Conventional secondary electron detectors include, but are not limited to, an Everhart-Thornley detector, a multichannel plate, a PIN detector, an avalanche diode, or APD. These detectors typically allow for the imaging of low energy secondary electrons from a metallic or hybrid semiconductor/metallic surface. However, the implementation of a protective and conductive pellicle film, positioned above the given photomask, has severely limited the ability of these conventional imaging approaches to image the photomask. Further, photomasks used in extreme ultraviolet (EUV) lithography require detection of defect particles as small as 10 nm in diameter, which further limits the usefulness of conventional electron imaging approaches in inspection of EUV-based photomasks.
As such, it would be advantageous to provide a system and method that provides improved electron imaging of photomasks through a protective pellicle so as to remedy the shortcomings of the conventional approaches identified above.